The invention relates to a method for operating an electron gun within a cathode-ray tube, and more particularly, to a method for controlling the electrodes of an electron gun to allow optimized operation of the gun for several operating modes, for example, in television mode and in monitor mode, in order to display high-resolution images of the SVGA or XGA type.
An electron gun generally consists of a zone called the beam-forming zone, forming a triode, comprising an emissive cathode, a first electrode G1, generally connected to a zero voltage, and a second control electrode G2, generally connected to a voltage of about a few hundred volts. In the case of a three-beam gun, for a trichrome tube, three emissive cathodes K are used to form three beams corresponding to the three primary colors to be generated on the screen, and the three beams pass through the grids G1 and G2, which are pierced, for example, with three holes arranged along the axes of said beams. Other electrode means, constituting a main lens, are arranged beyond the zone for forming the beam or beams, in order to focus the beams and/or to make the beams converge on the screen of the tube.
There is a rapidly growing tendency which requires the television tube, and the television set equipped with such a tube, to be able to display both television images and images arising from a multimedia application, in which the television set and its tube act as a microcomputer monitor.
However, although television images, for contrast and brightness reasons, are generated from high-current electron beams, high-resolution images for multimedia applications are, on the contrary, generated using low-current electron beams. This gives rise to a compromise problem in the design of the gun, since the known triode structure K, G1, G2 is suitable for one type of operation, but cannot be optimized for another, very different type of operation, for example, in a television mode or in a multimedia monitor mode.
The invention provides a simple solution to this problem, making it possible to optimize the operation of the gun for various types of images to be displayed on the screen of the tube, this being achieved by virtue of a structure of the beam-forming zone which allows the beam size to be adapted to various desired operating modes.
A method for operating a cathode-ray tube electron gun, wherein the gun comprises: a beam forming zone, for forming at least one electron beam, comprising in succession a cathode, and a plurality of electrodes with at least 2 control electrodes, and a main focusing zone consisting of at least one electrostatic lens. In the method, at least one variable potential is applied to at least one of the control electrodes of the beam-forming zone. This variable potential depends on the beam current so as to increase the size of the electron beam at the exit of the beam-forming zone for the low-current beams.